Flexible support material maintains disc height and supports the formation of hydrated tissue engineered intervertebral discs in vivo.

Background: Mechanical augmentation upon implantation is essential for the long-term success of tissue-engineered intervertebral discs (TE-IVDs). Previous studies utilized stiffer materials to fabricate TE-IVD support structures. However, these materials undergo various failure modes in the mechanically challenging IVD microenvironment. FlexiFil (FPLA) is an elastomeric 3D printing filament that is amenable to the fabrication of support structures. However, no present study has evaluated the efficacy of a flexible support material to preserve disc height and support the formation of hydrated tissues in a large animal model. Methods: We leveraged results from our previously developed FE model of the minipig spine to design and test TE-IVD support cages comprised of FPLA and PLA. Specifically, we performed indentation to assess implant mechanical response and scanning electron microscopy to visualize microscale damage. We then implanted FPLA and PLA support cages for 6 weeks in the minipig cervical spine and monitored disc height via weekly x-rays. TE-IVDs cultured in FPLA were also implanted for 6 weeks with weekly x-rays and terminal T2 MRIs to quantify tissue hydration at study endpoint. Results: Results demonstrated that FPLA cages withstood nearly twice the deformation of PLA without detrimental changes in mechanical performance and minimal damage. In vivo, FPLA cages and stably implanted TE-IVDs restored native disc height and supported the formation of hydrated tissues in the minipig spine. Displaced TE-IVDs yielded disc heights that were superior to PLA or discectomy-treated levels. Conclusions: FPLA holds great promise as a flexible and bioresorbable material for enhancing the long-term success of TE-IVD implants.